Life of Castertosk
by DeathhunterAshi
Summary: "Let yourself experience this, they said. The balance of the universe isn't that bad they said." Follow the adventures of Ratatosk, forced to be summoned into the Holy Grail War as a Caster-Class Servant by a unknown source with different Masters and situations. Much to his anger and reluctance that is.
1. First Appearance - Caster

-Summoning: Shirou Emiya-

 _He felt himself drifting instead of sitting in the center of the Ginnungagap, something that he strangely wasn't used to. A way to describe it would be...comforting._

 _But then he heard someone in distress. Someone was in trouble, but their resolve reminded him of someone he used to know. Someone he could never forget._

 _It was annoying, so he had to go and answer them._

"Hey...for disturbing my sleep, I'm going to kick your ass." His title had changed from "King of Monsters" to "Servant Caster". Wonderful.

The first thing Caster did was pull a sword from his sheath and parry the lance coming for the redhead, his Master's chest. Red eyes connected with the other's, earning a bloodthirsty grin from him.

"A Caster that uses a sword? This is the second Servant that uses a weapon outside of their assigned class." The one who was dubbed Lancer responded, backing away a little before getting back into position.

"Really? Then who was the first one you ran into?"

"An Archer that dual-wielded Falchions and wore red." Apparently this made the blond Caster click his teeth in annoyance before holding his longsword out for a new position much like Lancer.

"Great, he's probably got a hero complex like the last red-wearing dual-wielder I knew." And with that, they dashed forward.

Loud screeching of metal from the two weapons connecting with each other would have made others wince, but seemed to instead excite the two Servants- continuing their flurry dance of blades. Every swipe of a sword and thrust of a lance would be equally parried by the two, only scratches being found on their bodies. Whether it was from the fact that they were Heroic Spirits or the adrenaline, neither of them were tired from the force of fighting. Finally, Lancer jumped back and swung his spear down- going into a different position than before. He could see and feel the Mana swirling around him and backed off a little. If that connected...

"Sorry Caster, but I've got to end it here and now since 'Master' told me to hurry back. It was fun while it lasted though, its a hell of a lot better than running around observing people!" He yelled out as Caster glared at the activated Noble Phantasm, bringing his longsword in front of him instead of the backwards grip like before.

Damn...he could barely feel the Mana flowing from his connection with the red-haired kid.

"Gae..."

"Che, this is going to hurt."

"BOLG!" The bolt of energy from the thrust-forward spear rushed towards Caster as its 'cause and effect' happened, changing from 'the spear pierced the heart' to 'the spear has been thrust, therefore the heart must have been pierced'.

"Guardian!" He yelled out and a shine of a blue aura shield appeared in front of Caster's defensive position, almost being instantly destroyed upon Gae Bolg's connection. Caster grit his teeth, the force trying to push him back and destroy the arte-throwing as much Mana as he could into it before hearing a loud crack from the barrier.

Without thinking, he fell to the side-letting his right arm be pierced by Gae Bolg instead of his heart. It hurt like hell, but at least he was alive...or as alive as a Spirit could be. He was breathing heavily, cringing when he felt the cursed spear's power- not allowing himself the chance to be healed.

"Undodgeable? I want to punch the person who said it was possible. Guess I was lucky today in being a one-handed style swordsman." Caster, letting his currently useless arm dangle while his dominate hand still gripped his longsword (he was surprised that he was even still holding it) and felt the restorative effects of-

Wait, since when did he spawn with Nether Traitor and how had he not noticed in the rush of battle?

"Well, looks like that's my cue. My 'Master' is too much of a coward that he said if my attack fails then to come back." With that, Lancer jumped on the roof of the estate and turned- looking straight at Caster with a bloodthirsty grin on his face.

"Try not to die too early on Caster- I want to fight you again myself." This made the blond Summon Spirit grin viciously, practically matching Ireland's Child of Light's own.

"That goes to you too, Lancer." And with that, the Spear-wielding Heroic Spirit disappeared- taking off once in Astral Form.

* * *

Ashi: Hey there! I know its been a while since I've updated anything and most of my uncompleted chapters are in the Drive along with another side story. Basically this is a mini-series of Ratatosk as a Caster class Servant within different scenarios within the Holy Grail Wars, mostly the trilogy and Extra for now. For the next five chapters will lament of his and Shirou's relationship and interactions with other servants. After that will shift to another Master (who you probably already know from reading Caster isn' the best Class) and then to Hakuno.

Whether other TOS characters present will mostly likely be no due to it being Post-Game and over 1000 years passing. However, Tenebrae and Richter will be since they were in the Ginnungagap.


	2. Interaction - Shirou and Ratatosk

\- Master: Shirou Emiya-

* * *

"More." That was the simple command that Caster gave, holding the rice bowl in one hand while viciously rubbing evidence from his mouth.

Its only been a few days since Caster, whose true name was Ratatosk: the Lord of Monsters had been summoned to fight in the holy grail war by Shirou's side, something he was very confused about. Though all he said in response was "What? Were you expecting some other blond swordsman?" and proceeded to sheath his sword and huff a little. He felt a little sluggish, almost like the mana holding him to a contract was clogged up by something.

It would explain why his stats went down in that rank, lowering from EX to A.

"You have a surprisingly huge appetite, Caster. Though if I wasn't around Fuji-nee all the time, it would be even more astonishing." Shirou said, going to refill the bowl while muttering the last part. Not that it mattered since Caster heard it anyway.

"I'm keeping my reserves up since your summoning me blocked up most of the Mana connecting us. Its like being constipated from the start of waking up to next month, never able to actually take a crap." He shrugged, ignoring the redhead's surprise at how vulgar he was.

He had no reason to hide anything and since he was "officially" summoned, Gaia couldn't kick him out of this world.

"Wait, so your Mana is...clogged up? Why is that? Did something happen while you were fighting Lancer?" He almost stopped eating, but then vaguely shrugged, shrugged, knowing it wasn't that.

"When you called out and summoned me, your weak circuits flared out and took me from a weakened state. But you-" He said this while pointing the chopsticks at Shirou. "You don't even have your Mana Circuits fully opened all the way, making them from your nerves every single day! Its a surprise you're not dead over 500 times already!" That apparently took the redhead by surprise.

"Opened? I thought you just had to make new circuits every time you wanted to use magecraft." He was shocked definitely, but wasn't the whole motto of Magus being to walk with death? Ratatosk stared at his Master's expressions and figured out he wasn't naive, he was a freaking idiot in terms of magic!

"Listen clearly Emiya, since before the Great Kharlan War magic was used by elves, half-elves, dwarves, and monsters. Yet somehow there were humans born with the ability to harness said magic within their bodies without the need of modification or transfer until MUCH later. Though here on Gaia, Mana is drying out if the abundance of ley lines has anything to say about it. And unlike Aselia, there's no Summon Spirits here to regulate said energy equally you can kiss your sorry asses title in around 200 years, give or take the Holy Grail Wars." He slowly nodded, listening seriously to Caster's words as of his life depended on it. Which, in a way it did considering his attitude.

"So, if that's the case how do I unlock my...Prana? Also-" Reaching over with a napkin, Shirou wiped the sauce from Caster's mouth, earning a flinch and red eyes staring into golden ones.

"...Did you seriously just-"

"Sorry it was really bothering me."

The only thing that was heard next was a loud smack of hand against skin and a sharp yelp, Shirou rubbing his cheek and Caster reaching over for another bowl of rice.

"Anyway, there are three ways to transfer mana along with unlocking your initial prana. Sex, blood, and saliva. Unfortunately, there's no Rock 'n Roll involved. In your case, since no one told you about it in the first place, I'M going to have to do it for you the first time around." Caster responded while getting up, nearly ripping his Master's shirt off and placing a hand gingerly on his back.

"Hold on, wait we're doing this now?!"

"Would you rather wait until twin-tail tsunderbitch comes for your ass with the wannabe hero?"

"I...don't think Tohsaka-san is that bad." A soft crack could be heard from Caster's gloved hand that made Shirou seize up a little. A somewhat agitated mumble told him to calm down.

"Now I'm not going to bother wasting my time on lying. This is going to hurt, a lot. At the count of three I'll start." Well at least he was being nice about it.

"One-" And then with a rush of Prana forcing its way into his unopened circuits with the force of a tidal wave, Shirou screamed.

* * *

Well, that was a fine way to end a chapter off. By the way the chapters are pseudo chronological, so you front have to worry about getting lost. Also there are times where I'll switch from calling him Caster to Ratatosk so no need to really mind that!


	3. Berserker Battle - Shirou and Ratatosk

\- Master: Shirou Emiya-

Flipping around to dodge the oncoming attack, Caster felt his feet connect with the wooden trunk of a tree and pushed off it. Neither of them were expecting to suddenly be attacked by a loli controlling a behemoth with ease. Well, it was a fucking BERSERKER, what did he expect. Her giggling was annoying as hell and the whole woman-child thing was even worst, the only thing he was say was "Are you serious?"

Though add in more cursing and violence and you would get the gist to how Caster was acting.

"Uu hu hu, you're jumping around like a Squirrel so much even my Heracles is having a tough time catching you. But its still not enough!" Illyasviel von Enizburg said with a creepy smile on her face that made his eye twitch even more-

Why the hell did there have to be another Mithos in this damn world?! He was really starting to hate Gaia- frigid bitch.

Shirou, at least was now supporting him with arrows made from traced swords (some that probably shouldn't exist due to Ratatosk's interest with modern technology) - said traced bow "borrowed" from Archer when sending out his familiars to scout out during the last fight with this hulking Demi-God. How the hell was this kid even still standing up with all the Mana being sucked from her?!

One quick look and he rolled his eyes. She was a Homunculus. It was one thing or another wasn't it? First Replicas and then Androids...

Taking advantage of his distraction, Berserker rushed forward at a rate someone of his size shouldn't be able to achieve in the first place, slaming his slab of a sword into Caster's stomach- sending him flying with a jagged wound.

"CASTER!"

"Damn it Shirou, quit acting like he split me in half! Just focus on support!" He found himself growling lowly while his wound slowly healed, starting with internal injuries and leaving the heaviest for last. Jumping out the way again, he found himself in a power struggle, the mad servant's strength stat JUST above his as they fought tooth and nail, the Summon Servant glad for once he was never human.

Soon enough he got a fatal shot on Berserker, huffing a bit at the exertion of fighting this damn long aganist something that probably shouldn't even be that dexterous. But as being a Servant with E-Rank Luck and contracted with a Master that has E-Classed Luck, it was only a matter of time when he noticed the influx of Mana gathering around the corpse and-ARE YOU KIDDING ME RIGHT NOW.

"WHAT THE FUCK HE'S REGENERATING?!" Well it didn't take a genius or even Genis Sage himself to figure that out, but there has to be a limit to Maxwell-fucking Battle Continuation.

Before losing himself, instead he grined and pushed forward, pumping Mana into his legs and unleashing a barage of kicks to go with the numerous artes; the giant Demi-god roaring and fighting hard while recovering-something that didn't take as long as one would think it would. Though if that influx of Mana coming from two locations at the same time-

Archer, that motherfucker.

Sending three more darkness-infused Demon Fangs at Berserker, Caster grabbed Shirou and jumped up as far as he could, no time to pay attention to his Master's surprise.

"If you want to unleash a powerful as hell attack, now's the time to do so before that bastard comes after us and the Hero wannabe uses a high powered attack!"

"Wait, but what about Illya?!"

"What about her?! If he's like I've seen he is, then Berserker down there won't let her die. NOW HURRY UP!"

That got Shirou moving as he struggled in Caster's grip to get enough space to trace a crimson arrow filled with malevolent energy and the possibly of having a nasty curse on it? Oh who was he kidding, it DID have a nasty curse on it. In the distance, Archer stood at bay with his bow taut and ready to aim. With his ability he was able to clearly see the fight between Caster and Berserker take place, along with Shirou Emiya tracing swords with as much of a frequency as he did. This version of Caster he never encountered before, though if Alaya had anything to say about it, there was a bout of laughter from her and anger from Gaia. One who was amused by the Summon Spirit from another world and the other in a rage trying to eject him from the rules of the Holy Grail despite being "offically" summoned.

Even then, his mission didn't change from this unlikely variable- tracing the sword said to have killed the Hound of Chulain and notching it. The blast radius would take them out with ease, though dealing with Heracles would have to wait to be prioritized later.

At the same time Shirou pulled his own bow forward, the name of the traced weapon coming forward in his mind as Caster threw him higher, Ventus' core keeping them afloat. And while narrowing his eyes, both past and future let their arrows fly.

"CALDABOLG!"

"GAE BOLG!"

The two arrows hit their target and with it came an explosion loud and powerful enough to blast away a good portion of the forest and with it, making Shirou's ears ring. He felt himself falling before being caught by Caster and tucked into his arms instead of being carried like a potato stack like he always was. As this happened, his body jumped with the Summon Spirit kicking off the air again- heading in the direction of their home without looking back. He felt drained, using so much Prana during the fight and trying to get Illya to back down to no avail.

"Oy, you alright? Your ears didn't get injured with that blast, right?" Blinking, he didn't realize for a second that he was talking to him (though they were the only ones flying through the sky at the moment) and nodded. He didn't yell or huff indignantly like he usually did, instead holding onto the redhead a bit tighter and avoiding his more serious wounds. He knew he should have been recovering, but...

"I-I'm alright, now anyway. I wasn't expecting Archer to help us." That got a snort from the both of them. Archer actually helping? There's a unpleasant surprise.

"Please, he used a B-Ranked Broken Phantasm to do a wide-area attack. From the looks of it, Anti-Army." Well it worked in their favor in getting away. Hopefully it actually killed him this time. Tch, knowing that Servant it wouldn't die even if it was killed. "What matters is that we're alive and all that other motivational crap everyone says."

"Ah...you really can be nice as times despite how you act huh, Ratatosk?"

"Shut up or I'll drop you!" Truly the most tsundere of Spirits indeed.

Xx-Determination-xX

Ashi: I love writing fighting scenes in RP, not as well in Fanfiction.

Guest: Sorry, but I like making Shirou feel a bit of pain! Don't worry, the next chapter should make you smile!


	4. Misaki Town - Shirou and Ratatosk

-Master: Shirou Emiya-

"Let's go out." It was these very words that made Ratatosk drop the inari-zushi he was in progress of stealing off the plate. He blinked once, twice, three times before the words actively worked its way through his brain.

"The hell do you mean by go out?"

"Well ever since the fight with Berserker you either train or eat, not even watching tv like you did before. Besides being slapped by Tohsaka-san, you kind of seem down- Ratatosk." His eye twitched a little, ever since that night with Shirou getting bold enough to actually call him by his name and not the title the holy grail gave him. He snorted a little, looking to the side.

"Really? And where will we go this time since the park seems to be overly infested with the essence of a curse." He earned a small wince from that one and huffed indignantly. He knows that he's been a bit offensive the past few days, but there was something about this war that gave off a bad feeling, one that felt a bit too much like when Niflheim opened with his 'death'.

It was then he found himself yowling angrily when Shirou picked him up by his armpits like a child and proceeded to drag him to the borrowed room. And as expected: Ratatosk struggled.

"Let me go damn it! I don't want to go out right now!"

"If you keep staying in here, then you'll end up becoming a NEET of a Servant! And you've never Been in a world like this, now is the time to really get the chance to explore and experience things unlike from where you are from."

"WHY ARE YOU STUBBORN WITH STUPID SHIT LIKE THIS AND NOT WHEN BEING TREATING LIKE A KISS-ASS!"

And with much reluctance (from Ratatosk more than Shirou), the Master-Servant couple headed out from the Shinto district to Misaki City, Shirou wearing his usual outfit while Ratatosk was haphazardly stuffed into an altered gakuren with added headphones. Thankfully there was no school that day and Shirou managed to prevent the blond Servant from carrying a knife around and to tone down on the glowing eyes.

Once actually getting into the city, Shirou couldn't help but to notice his rather angry expression fading away to a more controlled curiosity like the first few days that they met. Whether it was from the amount of people here or the town itself was a question asked for later. Though with the way Ratatosk was moving through the street he had to practically hold his hand in order to catch up.

(Surprisingly, it didn't feel like hellfire and instead like the heat of a regular human being when not surging with raw Prana.)

Visiting a glasses shop, they found each other trying on different pairs for fun- though quickly putting down a pair that REALLY didn't suit him at all*; the blond wearing a pair of triangular glasses with a shit-eating grin on his face.

"Hey look at me, I'm Richter- shit eating edgelord of Asgard. I use a sword and axe simultaneously cause I think it looks cool to block a Summon Spirit's Mystic Arte!" Ratatosk taunted while wriggling his hips in a taunting fashion- the action causing Shirou to burst out laughing.

When they visited a stuffed animal store however, Ratatosk's mood became a bit melancholy when seeing a plush of a red-wearing boy with two swords and a green and white dog-looking monster. Before Shirou could see it though, he roughly shoved them back into the display and walked off with his hands in pockets. Looking back at the Servant and at the plush, he decided to secretly buy it before the other could turn around and scold him. As dusk rolled in, the two walked silently across the bridge before stopping halfway. Looking over the ocean as the wind blew through the open spaces, it was a quiet asylum from the fights they had been in for the past few days...It felt so much longer though.

"You're not as sneaky as you think you are, Shirou." Ratatosk's sudden response took him by surprise as he tried to hide to bag, but the blond was too quick- taking out the dog-like plush. And leaning lazily on his Master.

"You looked rather down when holding it so I though that getting it would make you feel better. With the War doing on, down time hasn't exactly been on our minds save for today." Frozen and kept in place by the taller man, Shirou sighed as one of his arms fell onto Ratatosk's back.

"Noishe was its name and its not a dog, its a monster known as a Protazoan; its been around as long as Mithos and his group were travelling around. Looking at it in a way just brought back some old memories." He tensed before just barely relaxing as a rough sigh made it out of him.

"Do you miss them?" That earned a sharp laugh out of Ratatosk.

"Like hell I do! But in a way, I kind of miss the weakling and Marta more than anything else."

The two of them stood there in the comfort of each other, much like after the fight with Berserker and didn't say anything for a while.

"If it makes you feel better, I MIGHT miss you too after this whole Holy Grail War shit is over. I'll be back on Aselia in the Ginnungagap and you'll be here with the tsundebitch and the homuculus brat." That earned a laugh from Shirou, who hugged him a bit tighter.

"I'll miss you too, Ratatosk. It won't be the same here without you."

Xx-Determination-xX

And we've only got one more chapter of Ratatosk being Shirou's Servant! It took a bit mostly do to inspration, but we're finally here! I ended up basing this more like the Stay Night/Saber Route more than the other ones. Also I was able to put in the plushie easter eggs since Tales of Symphonia came out a year before Fate/Stay Night- which was a surprise.

*The glasses that didn't fit Shirou at all was actually a reference to the UBW anime when he wore glasses similar to Tohno Shiki.


End file.
